This invention relates generally to a two-stage axial flow steering and propulsion device for watercraft, and more particularly to such device mounted for rotation in opposite directions about an axis intersecting with and perpendicular to the rotational axis of the impellers.
Several approaches are known from the prior art in the steering or the steering and propelling of watercraft for effecting shifts in the path of movement thereof especially along a confined and narrow waterway. Hazardous conditions which are to be avoided, particularly for barges and other marine craft of appreciable length, are collisions with other watercraft, high winds affecting control of the watercraft and collision with dock facilities while maneuvering the watercraft into and out of confined dock locations. The range of maneuverability of such watercraft is, however, limited with the use of known steering devices, and the capacity of the steering devices for effectively moving large volumes of water therethrough, is likewise limited by the particular characteristics of such devices.
A prior art steering unit for barges and the like is disclosed in U.S. Pat. No. 3,590,766, wherein the steering unit is fixedly mounted on a barge and has a two-stage axial flow impeller unit rotatably mounted within a tube for conveying water therethrough. A one-stage axial flow pump disclosed by U.S. Pat. No. 2,847,941 characterizes the improved pumping capacity of the two-stage steering unit of the U.S. Pat. No. 3,590,766. And a marine craft steering unit is disclosed in U.S. Pat. No. 3,850,132 as including a "bowl hull" having a pair of the U.S. Pat. No. 3,950,766 propulsion devices on opposite sides of the vertical rotational axis to effect propulsion of the hull and the connected barge upon actuation of the devices, rotation of the hull being carried out by actuation of one of the off-center devices.
Propulsion and/or steering devices as aforementioned are, however, limiting in their steering capability since they are basically non-rotatable about an axis extending through the impeller rotational axis, and the pumping capacity through the devices is limited because of their particular design.
A propulsion device for driving and controlling watercraft is disclosed in U.S. Pat. No. 3,893,405 as including a downwardly opening bell-shaped shield fixed to a hull, vertical baffle plates on the shield defining exit passageways for alignment with a centrally mounted pump having impeller blades rotatable about a vertical axis. The exit opening of the pump is aligned with one of the shield passageways for steering the watercraft, upon rotation of the pump. With such an arrangement, however, the propulsion device has a tendency to draw the watercraft down into the water since a vertical suction effect is produced. An alignment of the impeller nozzle with one of the shield passageways is basically ineffective and impractical in steering the watercraft because of the low pumping capacity made possible by such an arrangement.